[O] Pitch as used here, means vibration rate.
Transcriber's note:
This book uses B.T.U. and B.t.u., electrophorous and electrophorus, e.m.f. and E.M.F. and this has been left as written.
Hyphenation is also left as written, e.g. electro-plated and electroplated.
On page [324], Exercise number 8 was not used in the original. The exercises have not been renumbered.